import java.util.Scanner;

public class Main {
    static int N=110;
    static String s1;
    static String e1;
    static char[] s=new char[N];
    static char[] e=new char[N];
    public static void main(String[] args) {
        Scanner in =new Scanner(System.in);
        s1=in.nextLine();
        e1=in.nextLine();
        s=s1.toCharArray();
        e=e1.toCharArray();
        int step=0;
        for(int i=0;i<s1.length();i++){
            if(s[i]!=e[i]){
                step++;
                turn(i);
                turn(i+1);
            }
        }
        System.out.println(step);
    }

    static void turn(int i){
        if(s[i]=='*'){
            s[i]='o';
        }else {
            s[i]='*';
        }
    }
}